This invention relates to an internal combustion engine cooling system and in particular to improved means for filtering engine cooling air before it passes over a heat exchanger, such means being particularly useful on agricultural harvesting machines, such as combines and the like.
It has become conventional to at least partially enclose the engines of mobile harvesting machines and to mount a heat exchanger, such as a radiator, for cooling the engine within an enclosure. It is also well known to provide screens for filtering the cooling air drawn into the enclosure and also to provide means for removing from the screen accumulations of foreign materials, such as chaff and leaves, which occur in typical harvesting conditions.
Ideally, foreign material or trash removal should be automatic and continuous. Well known attempts to achieve this include the use of rotating screens in conjunction with baffles or ducts adjacent the screen to upset the flow of cooling air through the screen so that foreign material has an opportunity to fall off or be sucked off. U.S. Pat. No. 3,837,149, West et al, discloses a duct with an outlet end adjacent the engine cooling fan and an inlet opening adjacent to and spanning a portion of the rotating screen so that air is drawn through the duct and locally reverses the flow of air through the screen so that foreign material accumulated on the screen is removed and carried through the duct. However, it is generally necessary to provide a change of direction such as an "elbow" in such a duct and it is possible for some types of foreign material, such as elongated crop leaves, to lodge in the duct at the change of direction and create an obstruction which, in extreme conditions, may lead to a blocking of the duct, rendering the screen cleaner ineffective.
Another problem in the design of rotating cooling air screens is to provide an approximately flat but structurally stiff filter element while at the same time maintaining the maximum possible proportion of open area so as to achieve the maximum possible cooling system efficiency. It is known to use as a screen material a relatively stiff perforated metal sheet fabricated into a self-supporting cylindrical form. The extra total surface area of the cylinder compared with a given circular inlet opening compensates for the relatively low percentage open area of the material itself. However, such designs are inconveniently bulky are relatively costly to manufacture. It is also known to construct a flat rotary screen assembly using a more flexible, higher open area, material such as woven wire screen but it is difficult to provide a flat and stable screen surface even if the awkward and costly operations of stretching (and trimming) are used in its manufacture.